Quality and stability evaluation of Guizhou spicy chicken treated with gamma irradiation during the storage period

Abstract Irradiation has become a mature processing approach for the quality control of many agricultural products. The effects of gamma irradiation at four different doses (2, 4, 6, and 8 kGy) on microbial quality, Hunter's parameter, lipid oxidation, hydrolyzed amino acids (HAAs), and flavor in spicy chicken were investigated. After treatment, all samples were stored at 4°C. The microbiological results showed that the total viable bacteria (TVB) and total coliform count (TCC) were significantly decreased dose dependently. Values of Δa*, Δb*, and ΔE* of the irradiated specimens were lower compared with the control samples, whereas the ΔL* of the irradiated specimens was higher compared with the controls. The peroxide value (POV) was increased by dose augmentation. Contents of HAAs were gradually decreased in both irradiated and control groups. The odor was affected by both doses of irradiation and storage time. Hence, we conclude that irradiation at a dose of 4.0 kGy barely affected physicochemical properties during storage and extended the shelf life of spicy chicken. This approach could be an alternative to control the quality of spicy chicken during storage.


| Derivatization
Briefly, 50 μl of the sample was accurately taken and put into a 4-ml centrifuge tube. The tube was put into a vacuum drying oven at 60°C for 2 h, the centrifuge tube was filled with nitrogen, and then 50 μl of derivatization reagent (ethanol: phenyl isothiocyanate: water: triethylamine = 7:1:1:1) was accurately added. The solution was prepared just before use. It was filled with nitrogen during preparation and derivatized at room temperature for 30 min. Subsequently, 0.45 ml of mobile phase was added, and the mixture was mixed well and filtered through 0.25μm polyester filters.

| Determination
The amino acids of chicken meat were determined by highperformance liquid chromatography (HPLC) using Agilent 1260 HPLC (Agilent Technologies) system equipped with a ZORBAX 83 SB-C18 column (250 × 4.6 mm, 5 μm). The oven was operated at 40°C, and the sample injection volume was 10 μl. The mobile phase was composed of 97% of 0.1 M phosphate buffer solution (pH = 6.5) (A) and 5% methanol (B).

| Statistical analysis
The data were presented as mean ± standard deviation (SD), and the significant differences among the groups were analyzed by SPSS version 22.0 software (SPSS, Inc.) with 95% confidence. Data were analyzed by one-way analysis of variance (ANOVA) to test the treatment effect. E-nose data were processed by Win Musterversion 1.6 (Airsense Analytics Inc.). Mean separations were performed by Duncan's multiple range tests. Differences at p < .05 were considered statistically significant.

| Dosimetry
The actual absorbed dose may be different owing to the different positions of the sample in the basket. Therefore, the actual absorbed dose was measured by a solver dichromate dosimeter. The actual absorbed dose of four irradiated groups of the spicy chicken samples was 1.93, 4.12, 6.04, and 7.96.

| Microbiological test of irradiated chicken meat
TVB, TCC, Salmonella spp., S. aureus, and L. monocytogenes were measured, and Table 2  On the contrary, TVB in the 0 kGy and 2 kGy groups was increased during the whole storage time, and TVB of the 4 kGy group was gradually decreased until the 13th day and then increased in the rest storage period. TCC in four irradiated groups was always lower than 3.0 MPN/g during the whole storage period, and this value in the nonirradiated group was increased at 45 and 60 days.
The above results indicated that the irradiation dose greater than 6 KGy could inhibit the propagation of microorganisms in the spicy chicken, total coliforms seemed to be more sensitive to irradiation, and a dose of 2 kGy could control the growth of coliforms. A similar result has been found by Wellington et al. (2014) that low doses of gamma radiation can efficiently control pathogens in chicken meat. Moreover, gamma irradiation is the earliest irradiation method used in meat processing, which can not only control the growth of foodborne microorganisms but also improve the quality of meat (Hassanzadeh et al., 2017). Coliform is an indicator of fecal pollution. It exists in various environments and can be easily polluted in food processing. The effects of disinfection by radiation depend on the energy source, dose rate, and absorbed dose (Kyung et al., 2019). Xavier et al. (2016) have demonstrated that even 1.5 kGy of gamma irradiation is sufficient to eliminate enteropathogen from fresh chicken meat. The mechanism underlying the germicidal effect of irradiation is the ionization energy absorbed by DNA molecules. The phosphodiester bond in the DNA double helix structure is broken, resulting in the inability of cells to replicate themselves.

| Hunter's color
Spicy chicken contains a lot of chili oil, which is rich in red carotenoids, including capsanthin. Capsanthin is the primary color substance of mature pepper, which is primarily present mostly in both the free form and the esterified form with fatty acids. The values of ΔL*, Δa*, and Δb* represent lightness, redness, and yellowness, respectively. The color of spicy chicken was obviously affected by the four doses of irradiation ( Figure 1). The ΔL* values of the four irradiated groups were significantly higher compared with the nonirradiated group (p < .05). The change of ΔL * was not apparent in the 0 , 2 , and 6 kGy groups during the whole storage period.
In contrast, this value in the 4 kGy group was gradually increased, while it reached the minimum of 8 kGy on the 15th day after irradiation and then was gradually increased. At the end of storage, the value of ΔL* of the 4, 6, and 8 kGy groups was significantly higher compared with the control group and 2 kGy group. The value of Δa* was significantly (p < .05) decreased during the whole storage period compared with the control group. Moreover, the value of Δa* in the 6 and 8 kGy groups was dramatically decreased, which remained at  meat produced ROS when irradiated, and the double bonds and carbonyl groups in capsanthin reacted with ROS. However, the capsanthin in the dried red chili powder was not changed obviously after gamma irradiation. In our present study, the chili oil in spicy chicken samples faded, which might be attributed to the fact that the irradiation accelerates the automatic oxidation process of unsaturated fatty acids in the oil. Such a process produces many oxygen-containing products, such as hydroperoxides and carbonyl compounds, which can react with capsanthin and result in fading (Jung et al., 2015).

| POV
Chicken meat contains relatively high amounts of unsaturated fatty acids, making chicken meat considerably susceptible to deterioration caused by oxidation processes (Xiao et al., 2011). Peroxides are reported as the primary products of lipid oxidation. POV signifies the number of peroxides, which is an essential index for evaluating the storage stability of oils and fats (Gray et al., 1978 the degree of lipid damage caused by irradiation (Nisar et al., 2019).
Irradiation generates free radicals that can induce lipid peroxidation (Zheng et al., 2022).
Oxidative degradation of lipids from the spicy chicken was as-  The second cluster contained aliphatic amino acids (aspartic acid, glutamic acid, serine, glycine, arginine, threonine, alanine, proline, valine, methionine, cystine, isoleucine, leucine, and lysine). Table 3 shows that the HAA contents (g/100 g) were determined

| Hydrolyzed amino acids (HAAs)
in spicy chicken meat after being irradiated at four doses and stored for 60 days. All HAAs were decreased after irradiation and storage.
Aspartic acid, glutamic acid, serine, arginine, proline, valine, methionine, isoleucine, leucine, lysine, and histidine were not significantly changed at different irradiation doses with the same sampling time.

TA B L E 3 (Continued)
the 2, 4, 6, and 8 kGy groups at the end of storage time (60th day), respectively, which were decreased by 4.36%, 6.23%, 7.76%, and 9.07% compared with the control group, respectively. The effects of irradiation on aliphatic and aromatic amino acids are different (Jayathilakan & Sultana, 2018). The aromatic amino acids, including histidine, phenylalanine, and tyrosine, in all irradiated groups were decreased by 4.49%, 9.03%, 11.39%, and 13.34% compared with the control group at the end of storage, respectively. In contrast, the aliphatic amino acids were decreased by 4.35%, 5.95%, 7.39%, and 8.63%, respectively. The result demonstrated that the aromatic amino acids were more sensitive than aliphatic amino acids. and 7.37% of the total variance, respectively. The accumulative variance contribution rate of the two major components was larger than 90%, indicating that PC1 and PC2 covered the sample's prime information characteristics (Li et al., 2019). Clusters of 0 , 2 , and 4 kGy overlapped entirely, indicating that the flavor of chicken irradiated at these two doses was not distinguished from nonirradiated chicken. In contrast, clusters of 6 and 8 kGy were separated by the first two principal components. Moreover, the 6.0 kGy group exhibited a longer distance from the 0 kGy cluster compared with other doses, indicating that these two doses resulted in better discrimination than 0 kGy (Figure 4a). However, during 60 days of storage, four groups of irradiated chicken meat were separated from 0 kGy, showing a longer distance from 0 kGy based on PC1 (Figure 4b).
Therefore, the irradiation dose remarkably affected the flavor of spicy chicken during the storage period.

| LDA
The LDA method aims to construct a linear transformation to achieve maximum class discrimination by a linear combination of data (Zhou, 2017).

| LA
LA was conducted to identify the contribution of commonly used sensors responsible for distinction in PCA patterns (Zhang et al., 2007).
The contribution of each metal oxide semiconductor sensor to the F I G U R E 4 PCA plots of irradiated spicy chicken at different doses and storage time of 0 (a) and 60 days (b).
total response of the array could be judged by the location of the sensors in Figure 6. Sensors with loading parameters featuring a long distance to zero point indicate high contribution, whereas low values imply minor resolution of sensors (Li et al., 2019). Figure 6 shows the loading factors associated with PC1 and PC2 for each sensor. At the beginning of storage (Figure 6a), sensors W5W and W1W showed a relatively significant influence on PC1.
Meanwhile, W1W and W2W showed a vital influence on PC2.
Other sensors were close to zero point, suggesting minimal contribution. After 60 days of storage, sensors W5S and W1W still showed a relatively significant influence on PC1, and for PC2, W1W was changed significantly, exhibiting a longer distance from zero point than W5S. The sensor W2W also displayed a remarkable influence on PC2. Sensors W5S, W1W, and W2W responding to the odor of chicken meat were not changed at the beginning or end of storage, revealing that the characteristic odor of chicken meat was not shifted markedly after 60 days of storage.

| CON CLUS IONS
In conclusion, we showed that different doses of gamma irradiation significantly decreased TVB and TCC and prolonged the shelf life of spicy chicken meat during storage time. However, irradiation also affected the physicochemical properties of chicken meat. The color and odor of chicken meat were significantly changed in a dosedependent manner. In addition, the POV was significantly increased by 6 and 8 kGy of irradiation during the whole storage time, while irradiation had a slight effect on the contents of HAAs. Therefore, we recommended that preservation with gamma irradiation at 4.0 kGy could be an alternative to control the quality of spicy chicken during storage.

F I G U R E 6
Loading plots of irradiated spicy chicken at different doses and storage time of 0 (a) and 60 days (b).

CO N FLI C T O F I NTE R E S T
We declare that we have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available on request from the corresponding author.